ABSTRACT Mental health patients are twice as likely to smoke as those without mental health diagnoses and suffer from increased rates of tobacco-related mortality. Effective cessation treatments exist for mental health patients, but smokers with mental health conditions encounter low rates of tobacco screening and treatment by psychiatrists. The literature and our prior work have identified multi-level barriers to treating tobacco in psychiatry, and traditional opt-in tobacco treatment systems (where providers and patients must initiate treatment) can perpetuate these barriers. Opt-out systems (where patients are automatically enrolled in treatment unless they decline) have dramatically improved health-related behavior in other settings. We aim to conduct the first evaluation of an opt-out approach to tobacco treatment in outpatient psychiatry. We propose a mixed-methods, two-arm cluster-randomized pilot trial that will: (1) Estimate the effects of an Opt-Out versus Opt-In Tobacco Treatment System on the proportion of mental health patients who are screened and treated for tobacco use by their psychiatrist; (2) Assess intervention fidelity, provider perceptions of the Opt-Out System, and barriers and facilitators to implementation of the Opt-Out System; and (3) Estimate the effects of an Opt-Out versus Opt-In Tobacco Treatment System on use of cessation treatment and abstinence among mental health patients who smoke. We will use a mixed-methods, two-arm cluster-randomized study design. We will implement a tobacco use clinical reminder for outpatient psychiatrists practicing at the VA New York Harbor Healthcare System (N = 20). Half of the psychiatrists will receive a reminder that encourages the psychiatrist to offer cessation medications and referral to cessation counseling to patients interested in quitting (Opt-In Reminder). The other half will receive a clinical reminder that includes a standing NRT order and a referral to cessation counseling that will automatically generate unless the provider actively opts-out (Opt-Out Reminder). Prior to implementation, psychiatrists in both arms will receive a one-hour training on tobacco treatment and academic detailing. We will use VA administrative data to calculate the study's primary outcomes: 1) the percent of patients screened for smoking, 2) the percent of smokers prescribed a cessation medication and 2) the percent of smokers referred to counseling. We will use training logs and post-visit surveys with a cluster sample of 400 patients to assess intervention fidelity. We will conduct semi-structured interviews with 12-14 psychiatrists asking about their perceptions of the intervention components. We will also analyze implementation observations and documents for implementation barriers and facilitators. At six months, we will survey the clustered 400-patient sample again to evaluate the study's secondary outcomes: 1) patient use of cessation treatment in the prior 6 months and 2) self-reported 7-day abstinence at 6 months.